1. Field on the Invention
The present invention relates to a branched polycarbonate resin in which a content of gel like peculiar substances to exert an influence upon appearance and mechanical properties is small and a process for producing the same.
2. Prior Art
Hitherto, polycarbonate resin has been used in a wide range as engineering plastic excellent in transparency, mechanical strength and heat stability. Polycarbonate resin can be molded by various molding methods. Particularly, when a large type of molded article was produced by blow molding or extrusion molding, Newtonian flowability became problematic and the phenomenon of so called drawdown due to weight of polycarbonate resin itself often occurred, so that it was difficult to obtain an intended molded article.
Accordingly, in order to prevent the drawdown, polycarbonate resin to reveal non-Newtonian flowability to a great extent is preferable. As a process for producing a polycarbonate resin having such property, i.e., suitable structural viscosity, processes to use a branching agent are known For example, Japanese Patent Publication Nos. 44-17149 and 47-23918 disclose branched polycarbonate resins used phloroglucin, 4,6-dimethyl-2,4,6-tri-(4-hydroxyphenyl)-heptane-2,1,3,5-tri-(4-hydroxyphe nyl)-benzol, 1,1,1-tri-(4-hydroxyphenyl) ethane, trimelltic acid, etc, as branching agent When the branching agent was used, molding was improved. However, there occurred the problem that a portion of properties of polycarbonate resin thus obtained, particularly, impact resistance was decreased.
In order to solve the problem for improvement of impact resistance, Japanese Patent Publication Nos. 6-84429 and 7-103235 disclose arts in which molecular weight of branched polycarbonate resin is specified and acetone soluble component is limited. Although impact resistance at a low temperature was improved in the arts, effect of improvement of impact resistance at a room temperature was not satisfactory. Further, molded articles used branched polycarbonate resin sometimes provided scattering of impact resistance value, so that further improvement has been desired.
On the other hand, when branching in branched polycarbonate resin proceeded to an exceeding extent, the problem of generation of solvent insoluble gel occurred. Japanese Patent Publication Nos. 3-15658, 3-42288 and 4-69178 disclose branched polycarbonate resins in which generation of solvent insoluble gel has been depressed by specifying a process for production of branched polycarbonate resin. However, the definition of the gel was not clear and there was no disclosure concerning influence of the gel to exert upon properties of branched polycarbonate resin.